1. Field of the Invention
The present invention to a printing apparatus and an inspection method, and particularly, to a printing apparatus and a inspection method capable of performing a color shading inspection.
2. Description of the Related Art
In the inkjet type printing apparatus, there is known a technique for inspecting an ejection failure of a nozzle, landing-on accuracy of ink, and further, color shading. Specifically an inspection pattern is printed on a sheet and the inspection pattern is read by a scanner to inspect the ejection failure of the nozzle, the landing-on accuracy of the ink, and the color shading, thus performing a color shading correction.
In regard to the ejection failure of the nozzle or the landing-on accuracy of the ink, immediately after the inspection pattern is printed on the sheet, the sheet is conveyed, wherein the inspection pattern can be read by the scanner. However, the inspection pattern for detecting the color shading changes in color shading between a state where the ink is not yet dried immediately after the inspection pattern is printed and a state where the ink is dried. Therefore for accurately detecting the color shading, it is required to perform the inspection after the inspection pattern is dried.
Japanese Patent Laid-Open No. 2011-177954 discloses a technique in which a color shading inspection pattern is dried in a drying unit provided in a printing apparatus, and then the inspection pattern is read by the scanner. According to this technique, the color shading inspection pattern is conveyed in such a manner as to pass under the drying unit provided downstream of the scanner in the printing apparatus, and the sheet is conveyed in a direction opposing the conveying direction after all the regions of the inspection pattern are dried, to read the dried inspection pattern by the scanner.
In the apparatus disclosed in Japanese Patent Laid-Open No. 2011-177954, the sheet on which the dried inspection pattern is printed is reeled in a reeling unit and is afterward conveyed back to the upstream side of the scanner, wherein the inspection pattern is read by the scanner. However, there is a possibility that a conveyance misalignment of the sheet (position deviation or inclination of the sheet in the sheet width direction) occurs during the sheet conveying at the time of the conveying-back operation. When the conveyance misalignment of the sheet occurs, the inspection pattern also deviates from an original position. When the inspection pattern deviating from the original position is read by the scanner, a corresponding relation between the nozzle and the color shading inspection pattern is in error and therefore it is hard to accurately detect the actual color shading, leading to a possibility of performing an erroneous color shading correction.